The paths are a bit muddy at the moment, but otherwise the Haachts Broek is a lovely place to walk through. It’s quite an expansive area of deciduous woodland criss-crossed by small streams. There is a clearly signposted circular 5-km footpath that starts and ends at the sports hall in Wespelaar, where you can park if arriving by car. Otherwise the 284 De Lijn bus from Leuven stops at the sports hall. I haven’t found it yet, but there’s apparently an anti-tank ditch that in the spring is full of frogs and newts. What I did find is the Second World War bunker, which now holds a population of bats. In the spring the area is full of the songs of the usual woodland birds, although the golden oriole is reputed to nest in the area too, so that’s worth looking out for. Here’s a map: Haachts Broek map And here are some pictures.
Haachts Broek. Frogs, newts, tanks and bunkers

Looks like a very green surrounding there!
Yes Jacques; most of the pictures were taken last spring. It doesn’t look that green at the moment!